The present invention relates to a novel platinum(IV), herein also Pt(IV) or PtIV, complex and, more particularly, to a dihydroalkyl Pt(IV) complex, a method of producing same and a method of utilizing same in catalysis involving hydrocarbon activation and in reduction of organic molecules and of water to produce dihydrogen.
The direct, selective oxidation of alkanes has long been a major challenge in transition metal chemistry 1. The Shilov system, which employs chloroplatinum salts in aqueous media to catalytically functionalize methane, has been the subject of a number of mechanistic studies over the past few years 2. Unfortunately, unlike the classical Shilov system, most of the organometallic models used for these studies are extremely air- and moisture-sensitive. A key intermediate in this process was proposed to be an alkyl(hydrido)metal complex. Attempts to prepare such complexes under aqueous conditions resulted in platinum(IV)hydroxo complexes with concomitant release of hydrogen gas, probably via rapid hydrolysis of short-lived platinum(IV)hydrido intermediates 3,4. Consequently, most of the known hydrido(alkyl)platinum(IV) complexes were prepared and studied in the absence of oxygen and under anhydrous conditions. The dihydrido(alkyl)platinum(IV) complexes seemed to be more elusive than either the hydrido(alkyl)platinum(IV) or the dihydrido(dihalo)platinum(IV) complexes 5. Bercaw and coworkers, who studied extensively the individual steps of the catalytic oxidation of alkanes 6, have recently proposed a dihydrido(alkyl)platinum(IV) complex as a hypothetical intermediate in the low-temperature protonolysis of (PCy3)2Pt(H)R (R=CH3, Ph) which produced methane or benzene 7.
While reducing the present invention to practice a stable dihydrido(methyl)platinum(IV) complex, TpPtH2Me, 1 (Tp=hydridotris(Pyrazolyl)borate) was prepared via the reaction of TpPtMeCO, 2, with water. The resultant complex, 1, was unexpectedly found to be air- and moisture-stable and was found to contain not only two cis hydride ligands but also a cis methyl ligand.
A novel, air- and moisture-stable dihydrido(methyl)platinum(IV) complex, TpPtH2Me, 1 (Tp=hydridotris(pyrazolyl)borate) is formed as the sole product by the reaction of TpPMeCO, complex 2, with water. Complex 1 was structurally characterized by elemental analysis, 1H-NMR , 13C-NMR, and FTIR Without being bound to any specific theory, the proposed mechanism of the reaction of complex 2 and water involves an initial nucleophilic attack by a water molecule on the coordinated carbonyl in 2 with subsequent release of CO2 followed by protonation at the platinum center to produce complex 1. The resultant complex, 1, was unexpectedly found to be air- and moisture-stable and was found to contain not only two cis hydride ligands but also a cis methyl ligand.
Thus, according to one aspect of the present invention there is provided a platinum complex comprising a platinum(IV) metal center so positioned and oriented in the complex so as to complex in cis orientations with two hydride groups and with an alkyl, e.g., methyl, group, which complex can be in a solid state, e.g., crystallized, or dissolved as a portion of a solution.
According to another aspect of the present invention there is provided a solution comprising a solvent and a platinum complex therein in which a platinum(IV) metal center is complexed in cis orientations with two hydride groups and with an alkyl group.
According to yet another aspect of the present invention there is provided a method of preparing a platinum complex including a platinum(IV) metal center so positioned and oriented so as to complex in cis orientations with two hydride groups and with an alkyl group, the method comprising the step of contacting a platinum complex including a platinum(II) metal center being complexed with a CO group and the alkyl group and with water to thereby obtain the platinum complex including the platinum(IV) metal center so positioned and oriented so as to complex in cis orientations with the two hydride groups and with the alkyl group.
According to further features in preferred embodiments of the invention described below, the complex including said platinum(II) metal center complexed with the CO group and the alkyl group includes a nitrogen based polydentate ligand such as, but not limited to, hydridotris(pyrazolyl) borate, hydridotris(pyrazolyl) methane, aryltris(pyrazolyl) borate, aryltris(pyrazolyl) methane, heteroaryltris(pyrazolyl) borate, heteroaryltris(pyrazolyl) methane, alkyltris(pyrazolyl) borate and substitutes thereof, which serve as a complexing ligand (agent).
According to still another aspect of the present invention there is provided a process of activating a Cxe2x80x94C and/or a Cxe2x80x94H bond of a hydrocarbon, the process comprising the step of contacting the hydrocarbon with a platinum complex including a platinum(IV) metal center so positioned and oriented in the complex so as to complex in cis orientations with two hydride groups and with an alkyl group, thereby activating the Cxe2x80x94C and/or a Cxe2x80x94H bond of the hydrocarbon.
According to further features in preferred embodiments of the invention described below, the platinum complex includes hydridotris(pyrazolyl) borate, hydridotris(pyrazolyl) methane, aryltris(pyrazolyl) borate, aryltris(pyrazolyl) methane, heteroaryltris(pyrazolyl) borate, heteroaryltris(pyrazolyl) methane, alkyltris(pyrazolyl) borate and substitutes thereof.
According to still further features in the described preferred embodiments the hydrocarbon and the complex are in solution, the solution includes at least one substance selected from the group consisting of water, an alcohol, a ketone, aldehyde, an organic acid or any other organic molecule.
According to still further features in the described preferred embodiments the hydrocarbon is selected from the group consisting of an alkane, an alkene, an alkyne and an arene. Other hydrocarbons are also suitable, such as functionalized hydrocarbons.
The present invention successfully addresses the shortcomings of the presently known configurations by providing a novel platinum(IV) metal center complex characterized by cis orientated coordinative bonds with two hydride groups and with an alkyl group, which is both moisture and air stable and which can, therefore, be advantageously used for activating hydrocarbon Cxe2x80x94C and/or Cxe2x80x94H bonds and for reduction of organic molecules and of water to produce dihydrogen, for the production of a variety of useful chemicals